Steve Jobs thought he killed physical keyboards on smartphones when he introduced multi-touch with the iPhone in 2007, but four years later, many consumers still can't live without a tactile QWERTY. For PCs, the necessity of a full-sized keyboard is drastically more pronounced: Typing while viewing a full, unobstructed screen is, at this point, a prerequisite for almost any serious computing or communication activity. Since a tablet's slate-like form factor precludes it from including a dedicated keyboard, users looking to recreate a full computing experience have been forced to resort to peripherals... or just use their laptops.
Further, the current standard screen size for tablets of between seven and 10 inches leaves much to be desired. Many PC users either can't or won't trade in their big displays, which often represent an advantage in both content creation and consumption.